Feb. 22, 2013

Sea Nettles grow to about 4-inches wide at the cap and can have tentaces as long as 5 feet, stinging cells in the tentacles capture food or sting swimmers. / Digital Collections/IPTC

Stinging jellyfish called seanettles are thought to breed on plastic docks in Barnegat Bay. The jellyfish can have tentacles as long as 5 feet. Courtesy of National Aquarium in Baltimore The stinging jellyfish called seanettle is thought to possibly breed on plastic docks 2010 file photo -__-_Text: Sea Nettles grow to about 4 inches wide at the cap and can have tentaces as long as five feet, stinging cells in the tentacles capture food, but can sting swimmers who bump into the animals.--Courtesy of National Aquarium in Baltimore / Digital Collections/IPTC

SEA NETTLES

A notorious summertime pest in Chesapeake Bay, the stinging sea nettle jellyfish had a population explosion in Barnegat Bay starting in the middle of the last decade. Sea nettles are common in East Coast bay waters, but scientists don’t know why the Barnegat Bay population has grown so suddenly. Theories include ecological changes in the bay from increased stormwater pollution to overfishing that reduced other fish species and allowed jellyfish to take over. Some of the worst jellyfish summers here were 2010 and 2011 when parts of the northern bay were unswimmable for weeks. But jellyfish numbers appeared to be lower in 2012, according to researchers who track the population.

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Amid all the destruction that superstorm Sandy brought to Barnegat Bay, there’s been one quiet thread of speculation: could the storm with its massive, scouring surge from the ocean, have gotten rid of those jellyfish?

Stinging sea nettle jellyfish won’t appear in the bay until June, so it’s far too early to tell how the storm affected the population, scientists say. By the end of October when the storm arrived, the jellyfish were already at least a month into the winter dormant stage of their life cycle.

“We start to see the medusa (free swimming) population drop off the middle, end of September,” said Jim Vassilides, staff scientist with the Barnegat Bay Partnership, the federally funded office that coordinates research and conservation efforts on the bay.

As bay waters cool, swimming jellyfish lose energy and die off, leaving a huge population of tiny polyps – basically clusters of baby jellyfish that adhere to plastic docks over winter, and start popping out new swimming jellyfish in late spring and early summer.

The Virginia and Maryland waters of Chesapeake Bay are infamous for their summertime sea nettle swarms, and scientists there have observed fluctuations after major hurricanes. But timing is everything, says Rebecca Burrell, head technician of the marine ecology laboratory at the Smithsonian Environmental Research Center in Edgewater, Md.

“In general it’s not just the strength of the storm but the timing of a hurricane that plays a big factor in determining what is affected biologically,” Burrell said. Fresh water washing down into Chesapeake Bay from rainfall and reservoir release can reduce salinity levels in the bay “which can both reduce jellyfish polyps...and flush jellyfish out of systems.”

The best example was hurricane Agnes in 1972, a catastrophic event for the Chesapeake overall. Some 14 inches of rain fell in the bay watershed and flushed the bay, decimating salt water species. There was a dramatic reduction in sea nettles too, Burrell said.

The 1972 hurricane hit in June, just around the time sea nettle medusa starg swimming in the bay, Burrell noted. By contrast, hurricane Isabel i September 2003 had little effect. University of Maryland scientists “found no evidence of a hurricane effect on...sea nettles, but this time period is also when jellyfish populations are generally declining seasonally anyway,” she said.

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It’s possible Sandy’s rainfall may have reduced the numbers of jellyfish polyps, Burrell said. But becaus each polyp can pop out several swimming adult jellyfish come spring, “populations can rebound quickly because of the high reproductive potential,” she added.

“That polyp stage makes them highly resilient,” Vassilides said. During the Oct. 29 storm surge, “that volume of water moving through the bay might have dislodged some of them. We don’t know.”

Vinyl and other plastics had become materials of choice for docks, over chemically treated lumber, a trend encouraged by scientific studies showing treated lumber can have some negative effect on the bay environment.

So bayside residents were stunned to learn all those sleek new plastic docks are ideal nesting spots for jellyfish polyps, as Montclair State University Paul Bologna has documented.

Lots of docks were ripped out or scoured by rushing water and sand. “With all those docks that got tossed around, is that going to have an effect?” Vassilides wondered. There are other factors going into spring 2013, he added.

With warm bay waters and a warm summer in 2012, people braced for an even bigger swarm of jellyfish than the ugly summer of 2011 in the northern bay.

“But that was totally not the case,” said Vassilides, who heads a team that tests jellyfish-proofing nets at bay beaches, and works every day in summer to drag haul seines nets in the bay and count the nettles. The 2012 jellyfish numbers were substantially lower, and this could be a tough winter for polyps, he said.

“This winter is colder than the last couple of winters. The Toms River was iced over in some places,” he said.

Sea nettles made a first big appearance in northern Barnegat Bay in July 2004, raising dread among boaters and environmental experts who knew them as an annual summer plague on Chesapeake Bay.

Scientists still don’t know why their numbers exploded in Barnegat Bay. Theories range from the region’s rapid increases in storm water flows carrying nutrients to the bay from growing suburbs, to warming average water temperatures, and overfishing that removed other fish and helped the jellyfish take over.